1. Field of the Invention
This invention relates to methods and apparatus for manufacturing metallic pipe and other tubular products and, more particularly, to the handling of the hot pipe and other tubular products in transferring them from one mill to another mill.
2. Description of the Prior Art
Generally, there are two hot working methods for manufacturing metallic tubular products and pipes, the butt weld method and the seamless tube method. The butt weld method utilizes a forming and welding mill. Skelp passes through a forming stand that forces the skelp into an arc of about 270.degree.. Then the deformed metal edges pass over a welding horn and into a welding stand, where the edges are pressed together. Generally, a nozzle from the welding horn supplies oxygen to the edges of the skelp to further heat them before being pressed together. Further stands positioned downstream of the welding stand provide for reduction of diameter and a resultant change in wall thickness.
A stretch reducing mill may be utilized in series with the forming and welding mill to simultaneously reduce the diameter and the wall thickness of the tubular product by maintaining the tubular product under tension between mill stands.
Seamless tubular products are made by four basic methods: (1) rotary piercing of a solid round bar billet; (2) piercing a bloom or section of steel in a vertical press, leaving one end closed, and then processing by the roll forge process; (3) extruding a short, large diameter round in a hydraulic extrusion press; and (4) press piercing of a solid square billet. See The Making, Shaping and Treating of Steel, 10th Edition, .COPYRGT.1985, Chapter 32.
The present application is primarily directed to the butt weld method of forming pipe. Specifically, as shown in FIG. 1, a furnace 3 heats a straight piece of skelp as the skelp passes therethrough. The heated skelp, which is now in the hot working state, then enters the welding and forming mill 4 where the skelp is bent and edges are welded so that it is formed into a tubular product, such as a pipe. The tubular product is then cut to a predetermined length by a hot saw 5. A conveying table 6 then carries the tubular product to a cooling table.
However, should a steel mill want to modify this line to add a stretch reducing mill 10, then the line must be closed for months for modification and a second furnace 9 must be added at the end of conveying table 6. The second furnace heats the tubular product leaving the forming mill to a temperature which permits it to be hot worked before it then passes through a stretch reducing mill 10. The second furnace 9 is required because the tubular product cools to a point on the conveying table where it cannot be hot worked without being reheated prior to passing it through the stretch reducing mill 10.
The furnace 9 increases the cost of the finished product for several reasons: (1) the added fixed cost for the furnace; (2) the added cost due to the space requirements for the furnace; and (3) the added energy cost to heat the furnace.
Therefore, it is an object of our invention to provide a device that inexpensively transfers tubular products in a hot working state from one mill to another.
It is a further object of our invention to provide a device and method that passes tubular products in a hot working state from a welding and forming mill to a stretch reducing mill without the need to reheat the tubular product.
It is a further object of the present invention to provide a method and device that converts a welding and forming mill to a stretch reducing mill with a minimum amount of down time.